An anti-offset method for a wireless power transmission (WPT) system based on constant-voltage output interval tracking is proposed to deal with the problem of output voltage fluctuation when the coupling mechanism in the WPT system is shifted. First, a model of a CLC-S WPT system is established, and the relationship between the mutual inductance and output voltage gain in resonant and non-resonant states of the system is analyzed. Based on the analysis, it is found that the system has a stronger anti-offset capability in the constant-voltage output interval when it works in the non-resonant state. Second, an inductance compensation sequence is designed, and a constant-voltage output interval tracking control strategy is proposed to realize the constant output voltage control of the WPT system and improve its anti-offset capability. Finally, a simulation model and a test platform were built, and simulation and experimental results show that the constant-voltage output interval tracking control strategy can effectively reduce the output voltage fluctuation, thus verifying the robustness of the system under strong mutual inductance interference. Compared with the WPT system without constant-voltage output interval tracking, the CLC-S WPT system has a better dynamic regulation capability of output voltage.

An improved incremental conductance method with a variable step size is proposed to solve the problem that the traditional maximum power point tracking (MPPT) algorithm cannot strike a balance between the tracking speed and steady-state oscillation. The MPPT speed can be increased by the improved incremental conductance method using a zonal variable step size. Meanwhile, the steady-state oscillation problem is optimized by using the incomplete partial differential theory, thus improving the efficiency of photovoltaic power generation. The feasibility and effectiveness of the improved incremental conductance method is verified by comparing the traditional control algorithm with the improved incremental conductance method.

Aimed at the problem of eddy current loss, a method for the parameter design and optimization of a wireless power transfer (WPT) system in seawater is proposed to optimize the power transmission efficiency of the system. First, based on the analysis of the electromagnetic field of coils under operation in seawater, the equivalent mutual inductance model of the WPT system in a marine environment is obtained by using the equivalent impedance of eddy current loss. Second, when the positions of the primary- and secondary-side coils are fixed, the corresponding relationship between the equivalent impedance of eddy current loss and the operating frequency of the system and the number of coil turns is established, and the feasibility of the calculation method for the equivalent impedance of eddy current loss is verified by using the coils on both sides of the WPT system. Finally, based on the energy model of an LCC/S-type WPT system in seawater, the particle swarm optimization algorithm is used to optimize the transmission efficiency. A test system was built with the optimized parameters, and results show that when it transmitted 1 kW of power in a simulated marine environment, its overall efficiency can reach 84%.

To enhance the accuracy of a lithium battery model and realize accurate state estimation of the lithium battery, a fractional-order electric model of the lithium battery was built, and the model parameters were identified using adaptive genetic algorithm. Based on the fractional-order electric model, the unscented Kalman filter was adopted to estimate the lithium battery’s state-of-charge (SOC) and state-of-health (SOH). Stimulation results show that, the established fractional- order electric model of the lithium battery can more accurately describe its dynamic characteristics during charging and discharging, and the accuracy of the proposed state estimation strategy was higher than that the conventional control strategy.

Aimed at the problems of current unobservable area and zero drift error in the traditional space vector pulse width modulation with single-sensor phase current reconstruction method, an error self-correction complementary non-zero vector pulse width modulation method is proposed. Through the analysis of the DC bus sample principle, the minimum sample time is defined, the complementary non-zero vector is used to replace the zero voltage vector, and the current sampling window is extended, thus eliminating the sector boundary unobservable area. At the same time, the generation mechanism of error amplification effect is revealed, and the zero drift is detected and self-corrected by means of double-sampling complementary non-zero vector, which realizes the compensation for current zero drift reconstruction. Experimental results show that the reconstruction error of the proposed method was lower than 1.26%, and the phase current THD was lower than 6.15%.

As the penetration rate of renewable energy resources in a new power system continues to rise while the proportion of traditional thermal power units continues to decline, the new power system faces severe frequency control problems. Distributed battery energy storage systems (BESSs) provide an effective way to solve these problems. On this basis, a robust load frequency control (LFC) method for distributed BESSs based on sparse communication network is proposed. To suppress the uncertainties related to system operation, a two-tier model predictive control (MPC) is designed to improve the response characteristics of BESSs, thus improving the performance of LFC. To minimize the area control error, the proposed method can satisfy various operating physical constraints of the system. In addition, the influence of communication delay on the performance of frequency modulation participated by BESSs is also considered, and a fuzzy coordination control device is designed to coordinate BESSs and the traditional generator, so that the mis-operation of the traditional generator under the condition of long delay can be avoided. Finally, simulation results show that the response capability and frequency modulation effect of distributed BESSs are better than the traditional methods under parameters such as different values of capacity, rated power, charge and discharge coefficient, state-of-charge and time constant.

Aimed at the problems of DC bias and frequency variation in a weak grid, a modified inverse Park transform phase-locked loop (IPT-PLL) technology suitable for single-phase grid-connected inverters is proposed. First, the α component after Park transform is used as a reference voltage in the phase detector to solve the problem of DC bias in grid voltage, and an orthogonal component is constructed by the method of 1/4 fundamental periodic delay. Second, the fractional-order delay is approximated by Lagrange interpolation polynomial to reduce the calculation error of delay caused by frequency variation, and the design method for PI regulator is theoretically analyzed. Finally, experimental results show that the modified IPT-PLL proposed has a strong frequency adaptivity, and it can significantly suppress the interference of DC bias in grid voltage. In addition, its dynamic and static performances are satisfying.

Aimed at the problem that the accuracy of photovoltaic array fault diagnosis based on support vector machine (SVM) is not high and it is easily affected by the kernel function and penalty factor parameters, a photovoltaic array fault diagnosis method based on SVM optimized by the seagull optimization algorithm (SOA) is proposed. The SOA is introduced to optimize the parameters of the SVM model, and an SOA-SVM fault diagnosis model based on the optimal parameters is established. MATLAB software is used to build a photovoltaic array simulation model, and the characteristic parameters under different fault types are extracted and further inputted into the SOA-SVM model for fault diagnosis. Experimental results show that the fault diagnosis accuracy of the SVM model optimized by SOA is significantly improved. Compared with the ABC-SVM and PSO-SVM models, the SOA-SVM model converges faster in the optimization process and has a higher fault diagnosis accuracy.

With the scale expansion of a subsea observation network, the stability of its high-power power supply system has attracted attention. First, the impedance models of key parts in the subsea power supply system are established. Considering the characteristics of high power electronic penetration rate, multi-bus cascading and adjacent bus interactive coupling of the subsea DC power supply system, the stability and influencing factors of the system are explored by using the step-by-step analysis method. The analysis result shows that the integral parameter of the controller is the dominant parameter that leads to the instability of the Buck converter, and the proportional parameter of the controller is the dominant parameter that results in the instability of the junction box subsystem. Both an increase in the impedance parameter of the optoelectronic composite cable and a decrease in the inductance parameter are beneficial to improving the system stability. The simulation results based on the PLECS simulation software verify the stability analysis results.

For a hybrid cascade H-bridge inverter with a DC-side voltage ratio of 1:1:2, if the hybrid carrier disp-osition modulation strategy is adopted, the problem of output power imbalance in the low-voltage unit will occur al-though there is no current backflow phenomenon and the harmonic performance of output voltage is good. To solve this problem, the power imbalance is analyzed at first. Then, an improved hybrid modulation strategy is proposed, under which the high-voltage unit performs step wave modulation and the low-voltage unit performs PWM, and two low-voltage units adopt different processing methods for the modulation wave. The good harmonic performance of output voltage is kept, the number of triangular carriers is reduced, and the control process is simplified, with a frequency doubling effect. Third, this strategy is optimized, and the switching signal of low-voltage unit is logically calculated, which can solve the power imbalance problem of low-voltage unit in two carrier cycles. Finally, the feasibility was proved by simulation and experimental results.